JP2015513444A - Method for preparing an aqueous solution comprising at least one alkaline earth metal bicarbonate and use of the aqueous solution - Google Patents

Abstract

The present invention relates to a method for preparing an aqueous solution comprising at least one alkaline earth metal bicarbonate and the use of the aqueous solution. The process can be carried out in a reactor system equipped with a tank (1) fitted with a stirrer (2), at least one filtration device (4) and a grinding device (18).

Description

  The present invention relates to the field of methods of making alkaline earth metal bicarbonate aqueous solutions and the use of such solutions.

  Calcium carbonate is widely used as a paper filler component in the paper industry. This is a low cost, high brightness filler used to increase the brightness and opacity of the paper. This use has increased dramatically in recent decades due to the conversion of acid paper to neutral paper in paper mills. The paper industry uses both natural and synthetic calcium carbonates. Natural carbonate or limestone is ground to a small particle size before use in paper, but synthetic calcium carbonate is produced by a precipitation reaction and is therefore referred to as precipitated calcium carbonate (PCC).

  In addition to use in the paper industry, precipitated calcium carbonate is also used for various other purposes, such as fillers or pigments in the paint industry, and plastic materials, plastisols, sealing compounds, printing inks, rubber, toothpaste, cosmetics. It is also used as a functional filler for the production of foods and pharmaceuticals.

  Precipitated calcium carbonate exists in three main crystalline forms: calcite, aragonite and vaterite, each of which has many different polymorphs (crystal habits). Calcite has typical crystals such as canine (S-PCC), rhombohedral (R-PCC), hexagonal columnar, table-like, colloidal (C-PCC), cubic and ridged columnar (P-PCC). It has a trigonal structure with a wrinkle. Aragonite has a variety of varieties, including hexagonal columnar typical crystal habits and thin and elongated ridge columns, curved blades, pointed pyramids, chiseled crystals, branched dendrites and coral or worm-like forms. It has an orthorhombic structure.

PCC is usually prepared by introducing CO ₂ into an aqueous suspension of calcium hydroxide (so-called lime milk).
Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O

Numerous patent applications describing the preparation of precipitated calcium carbonate are known to those skilled in the art. This example is EP1966092B1, in this case, precipitated calcium carbonate obtained is only by-products of the CO ₂ sequestration. Another example is WO2010 / 12691, which discloses the preparation of PCC by adding alkaline earth metal hydroxide to water containing alkaline earth metal ions.

For example, international patent application WO2006 / 008242A1 describes the production of high purity calcium carbonate or magnesium carbonate from a feedstock containing Ca- or Mg-containing mixed metal oxides, where CO ₂ is To isolate, the feedstock is contacted with a CO ₂ containing gas, and in a further step, high purity calcium carbonate or magnesium carbonate is precipitated from an aqueous solution obtained by contacting the feedstock with CO ₂ .

  In addition to the above fields, calcium carbonate can also be used in the fields of water treatment and mineralization.

  Drinking water is running out. Even in water-rich countries, not all water sources and reservoirs are suitable for drinking water production, and many water sources today are at risk of dramatic water quality degradation. Initially, the water used for drinking purposes was mainly surface water and groundwater. However, for environmental and economic reasons, the treatment of seawater, brine, brackish water, wastewater and contaminated effluent is becoming increasingly important.

  Several methods are known for recovering water from seawater or brackish water for potable use, which are very important for dry, coastal and offshore islands, such as distillation, Includes electrolysis and osmotic or reverse osmotic pressure methods. The water obtained by such a process is very soft and does not contain pH buffer salts, so it has a low pH value and therefore tends to be highly reactive and transported in conventional pipelines if not treated. Serious corrosion problems can occur inside. Furthermore, untreated desalinated water cannot be used directly as a drinking water source. It is necessary to mineralize the water in order to prevent dissolution of undesirable substances in the pipeline system, to avoid corrosion of waterworks such as pipes and valves, and to improve the mouthfeel of the water.

  Conventional methods mainly used for water mineralization are lime dissolution with carbon dioxide and limestone bed filtration. Other less common remineralization methods include, for example, the addition of slaked lime and sodium carbonate, the addition of calcium sulfate and sodium bicarbonate, or the addition of calcium chloride and sodium bicarbonate.

The lime method involves the treatment of a lime solution with CO ₂ acidified water, with the following reactions:
Ca (OH) ₂ + 2CO ₂ → Ca ²⁺ + 2HCO ₃ ⁻

As inferred from the above reaction scheme, 2 equivalents of CO ₂ are required to convert 1 equivalent of Ca (OH) ₂ into Ca ²⁺ and bicarbonate ions for ^{remineralization} . This method relies on the addition of 2 equivalents of CO ₂ to convert alkaline hydroxide ions to the buffer species HCO ₃ ⁻ . For remineralization of water, 0.1 to 0.2% by weight of saturated calcium hydroxide solution (commonly referred to as lime water) relative to the total weight of lime milk (usually at most) 5% by weight). Therefore, a saturator must be used to make the lime water, and a large volume of lime water is required to achieve the target remineralization level. A further disadvantage of this method is that slaked lime is corrosive and requires proper handling and specific equipment. Furthermore, insufficient control of slaked lime addition to soft water can lead to unwanted pH shifts due to the absence of lime buffering properties.

The limestone bed filtration method includes a step of passing soft water through a granular limestone bed to dissolve calcium carbonate in a water stream. When limestone is contacted with CO ₂ acidified water, the water is:
CaCO ₃ + CO ₂ + H ₂ O → Ca ²⁺ + 2HCO ₃ ⁻
According to mineralization.

Unlike the lime method, only one equivalent of CO ₂ is stoichiometrically required to convert one equivalent of CaCO ₃ to Ca ²⁺ and bicarbonate ions for remineralization. Furthermore, limestone is not corrosive and a large pH shift is suppressed due to the buffering properties of CaCO ₃ .

One of the additional advantages of using calcium carbonate over lime is this very low carbon dioxide footprint. 75 kg of CO ₂ is released to make 1 metric ton of calcium carbonate, while 750 kg of CO ₂ is released to make 1 metric ton of lime. Thus, the use of alkaline earth metal carbonates such as marble, dolomite or (or only have) calcined dolomite instead of lime presents several environmental benefits.

  However, the dissolution rate of granular calcium carbonate is slow and this method requires a filter. This induces a fairly large footprint of such a filter and requires a large factory surface for the limestone floor filtration system.

  Methods for remineralizing water using lime milk or lime slurry are described in US 7,374,694 and EP 0520826. US 5,914,046 describes a method for reducing the acidity in an effluent stream using a pulsed limestone bed.

WO 2010/12691 discloses a method for treating water containing at least a calcium salt and / or a magnesium salt with a reverse osmosis type (typ) membrane. The method comprises at least one step of recovering at least partially desalted water, a step of recovering a concentrate obtained from the membrane and containing bicarbonate, and CO ₂ or acid is at least partially desalted. Injecting into water, and remineralizing the at least partially desalinated water. CO ₂ is added to the bicarbonate solution to decarboxylate the concentrate and to form a calcium carbonate mass from the bicarbonate.

  The applicant is also aware of the following unpublished European patent applications in the field of water treatment.

  European Patent Application 111755012.1 describes a process for remineralizing desalinated fresh water containing a constant carbon dioxide level by pouring a slurry of micronized calcium carbonate into the feed water.

  European patent application 10172771.7 describes a process for remineralizing fresh water by injecting a slurry of finely divided calcium carbonate.

  Finally, European patent application 11179541.5 describes a method for remineralizing water by combining a calcium carbonate solution and feed water.

  The three unpublished European patent applications in the water treatment field do not indicate anything about the specific surface area (SSA) of the alkaline earth metal carbonate used. From the average particle size mentioned in the examples of these patent applications it is not possible to calculate the specific surface area (SSA) of the corresponding product. Nothing is shown regarding the effect of specific surface area on the efficient preparation of alkaline earth metal carbonate solutions. There is also no indication of parallel in situ particle division to improve the method.

European Patent No. 1966092 International Publication No. 2010/12691 International Publication No. 2006/008242 US Pat. No. 7,374,694 European Patent Application No. 0520826 US Pat. No. 5,914,046 International Publication No. 2010/12691 European Patent Application No. 111755012.1 European Patent Application No. 10172771.7 European Patent Application No. 11179541.5

  Thus, in light of the shortcomings of known methods for water mineralization or remineralization, the object of the present invention is to provide an alternative and improved method for water mineralization.

  Another object of the present invention is that no corrosive compounds are required, thus avoiding the danger of incuration, no need for corrosion resistant equipment, and a safe environment for people working in the factory. Is to provide a method for water mineralization. It would also be desirable to provide a method that is environmentally friendly and requires less carbon dioxide when compared to current water remineralization by the lime method.

  Another object of the present invention is to provide a method for mineralization of water in which the amount of mineral can be adjusted to the required value.

The foregoing and other purposes are:
a) preparing water;
b) providing at least one substance comprising at least one alkaline earth metal carbonate and optionally a small amount of at least one alkaline earth metal hydroxide relative to the alkaline earth metal carbonate, The at least one substance is in dry or aqueous form, step c) providing CO ₂ ;
d) (i) the water of step a), at least one substance comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide of step b), and step c) with CO ₂ , or (ii) the water of step a) and at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide of step b). Combined with at least one material comprising, obtaining an alkaline aqueous suspension of at least one material comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide Either subsequently combining the alkaline aqueous suspension with the CO _{2 of} step c) to obtain a product suspension S having a pH of 6 to 9, wherein the product suspension The suspension S contains particles, a process,
e) A step of filtering at least a part of the product suspension S by passing at least a part of the product suspension S through a filtration device to obtain an aqueous solution containing at least one alkaline earth metal hydrogen carbonate. ,
f) a step of subjecting at least part or all of the particles of the generated suspension S to a particle fragmentation step,
Here, step f) can be carried out before and / or in parallel with and / or after step e),
Here, the particles of the product suspension S obtained in step d) exhibit a total particle surface area (SSA _total ) of at least 1000 m ² / product suspension S metric tons,
However, the addition of CO _{2 in} step c) is prior to the addition of at least one substance comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide in step b). It is solved by providing a method for preparing an aqueous solution containing at least one alkaline earth metal hydrogen carbonate, provided that it is not carried out in the first step.

  If the specific surface area of the material comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide is known, the total particles of the alkaline aqueous suspension of step d) The surface can be easily adjusted. Alternatively, the specific surface area of the material comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide is known to those skilled in the art and is defined in Standard ISO 9277. Should be sought by different methods.

  According to another aspect of the present invention, there is provided the use of an aqueous solution comprising at least one alkaline earth metal bicarbonate for the preparation of precipitated alkaline earth metal carbonates, in particular for the preparation of precipitated calcium carbonate. .

  According to yet another aspect of the invention, there is provided the use of an aqueous solution comprising at least one alkaline earth metal bicarbonate for the production of precipitated hydromagnesite.

  According to a further aspect of the invention, there is provided the use of an aqueous solution comprising at least one alkaline earth metal bicarbonate for the mineralization of water.

In another aspect of the present invention,
I) the process of preparing the feed water,
II) a step of preparing an aqueous solution containing at least one alkaline earth metal bicarbonate; and III) a feed water of step I) and an aqueous solution containing at least one alkaline earth metal bicarbonate of step II) A method for mineralizing water is provided, including a step of obtaining mineralized water by combining together.

Another aspect of the present invention provides:
IV) a step of preparing an aqueous solution containing at least one alkaline earth metal hydrogen carbonate, and V) heating the aqueous solution containing at least one alkaline earth metal hydrogen carbonate in step IV) to prepare precipitated alkaline earth. And / or VI) adding at least one alkaline earth metal hydroxide or alkaline earth metal oxide to the solution of step IV) to obtain a precipitated alkaline earth metal carbonate. A method for producing a precipitated alkaline earth metal carbonate comprising a step.

  Advantageous embodiments of the invention are defined in the corresponding subclaims.

According to one embodiment of the invention, the particles of product suspension S have a range of 5000 to 5000000 m ² / product suspension S metric tons, preferably 10,000 to 5000000 m ² / product suspension S metric tons. More preferably, a total particle surface area (SSA _total ) ranging from 70,000 to 500,000 m ² / S metric tonnes of product suspension, eg, 100,000 to 500,000 m ² / metric tons.

According to another embodiment, the at least one substance of step b) comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide is marble, limestone, Chalk, semi-calcined lime, calcined lime, dolomite limestone, calcareous dolomite, semi-calcined dolomite, calcined dolomite, and precipitated alkaline earth metal carbonates such as precipitated calcium carbonate of calcite, aragonite and / or vaterite mineral crystal structures Selected from the group comprising (e.g. by softening of water by addition of Ca (OH) ₂ ). The use of marble, limestone, chalk and dolomite is preferred because they are naturally occurring minerals and at least one alkali produced with such naturally occurring minerals. It is because the turbidity of the quality of the final drinking water is guaranteed by using the transparent aqueous solution containing the earth metal hydrogen carbonate. Natural marble deposits usually contain acid-insoluble silicate impurities. However, when using products prepared by the process of the present invention, such acid insoluble, optionally colored silicates do not affect the final water quality with respect to turbidity.

  Also, suspensions or solutions prepared by using naturally occurring minerals such as marble, limestone, chalk or dolomite contain essential health trace elements that improve the quality of drinking water .

Optionally, the at least one alkaline earth metal hydroxide is preferably calcium hydroxide and / or magnesium hydroxide. Due to the fact that the solubility of Mg (OH) ₂ in water is very low compared to Ca (OH) ₂ , the rate of reaction of Mg (OH) ₂ with CO ₂ is very limited, and Ca in suspension _(OH) reaction between CO ₂ and Ca _{(OH) 2} may become extremely very preferably in the presence of _2. Surprisingly, by using the method of the present invention, an alkaline earth metal hydrogen carbonate suspension with a high content of Mg (HCO ₃ ) ₂ even if Ca (OH) ₂ is also present in the suspension. Can be produced.

According to another embodiment, the at least one substance of step b) comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide is from 0.1 μm. It has a weight median particle size (d ₅₀ ) in the range of 1 mm, preferably in the range of 0.7 μm to 100 μm.

The at least one substance of step b) comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide is preferably from 0.01 to 200 m ² / g. One having a specific surface area in the range, more preferably in the range 1 to 100 m ² / g, for example 1 to 15 m ² / g.

The term “specific surface area (SSA)” refers in the sense of the present invention to the pigment / mineral / solid material properties measured in terms of surface area per gram of pigment. The unit is m ² / g.

The term “total particle surface area (SSA _total )” in the sense of the present invention denotes the total surface area per metric ton of suspension S1.

  In a preferred embodiment of the invention, the at least one substance of step b) comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide is a total dry substance. It has a hydrochloric acid (HCl) insoluble content of 0.02 to 90% by weight, preferably 0.05 to 15% by weight. The HCl insoluble content can be, for example, minerals such as quartz, silicates, mica and / or pyrite.

  According to yet another embodiment of the invention, the product suspension S obtained in step d) is in the range of 0.1 to 80% by weight, preferably the total weight of the product suspension S, preferably Those having a solids content in the range of 3 to 50% by weight, more preferably in the range of 5 to 35% by weight.

  The water of step a) is preferably selected from distilled water, tap water, desalinated water, brine, treated waste water or natural water, such as ground water, surface water or rain water. Moreover, 10 to 2000 mg NaCl per liter may be contained.

According to one embodiment of the invention, CO ₂ is selected from gaseous carbon dioxide, liquid carbon dioxide, solid carbon dioxide or a gaseous mixture of carbon dioxide and at least one other gas, preferably gaseous carbon dioxide. It is. When CO ₂ is a gaseous mixture of carbon dioxide and at least one other gas, the gaseous mixture is a carbon dioxide-containing exhaust that is emitted from an industrial process or similar process such as a combustion process or a calcined process. It is smoke. Further, CO ₂ may be produced by a reaction between an alkali metal carbonate and / or an alkaline earth metal carbonate and an acid. Furthermore, it may be produced by burning organic matter such as ethyl alcohol, wood or by fermentation. When using a gaseous mixture of carbon dioxide and at least one other gas, the carbon dioxide is present in the range of 8 to about 99% by volume, preferably in the range of 10 to 25% by volume, for example 20% by volume. According to one highly preferred embodiment, the CO ₂ is pure gaseous CO ₂ having a purity of> 99%, for example> 99.9%.

In view of the ecological concept, the CO ₂ used in the process has a decay from ¹⁴ C to ¹² C of at least 500, more preferably at least 800, most preferably at least 850 per gram of C in CO ₂ per hour. to have a collapse of 890 from following the Kyoto Protocol as possible with respect to the reduction of combustion of petrochemicals sources, and it is desirable to reduce the CO ₂ from petrochemicals.

  It is also desirable in accordance with the Kyoto Protocol to obtain at least some or all of the power used in the method of the present invention from solar power generation, such as thermal and / or voltammetric solar panels.

In a further preferred embodiment of the invention, according to the Kyoto Protocol, the amount of CO ₂ used to produce 1 mol of the at least one alkaline earth metal bicarbonate in aqueous solution is in units of mol It is in the range of 0.5 to 4 mol, preferably in the range of only 0.5 to 2.5 mol, more preferably in the range of only 0.5 to 1.0 mol, most preferably in the range of only 0.5 to 0.65 mol. .

  The method according to the invention comprises a step f), in which all or part of the product suspension S is subjected to a particle fragmentation step of the particles contained in the product suspension S. The particle fragmentation step f) may be performed before step e), may be performed in parallel with step e), may be performed after step e), or performed before and after step e). Also good. In a preferred embodiment, the particle fragmentation step f) is a grinding and / or grinding step, most preferably a grinding step. By this step, a fresh and thus active surface of the material comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide is continuously produced, The benefit is that the (chemical) reaction rate of the process of the invention is increased. This process step also reduces the size of the particles of the substance of step b) comprising an alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide, so that the process can be carried out continuously. Is possible.

  The term “milling” is used in the sense of the present invention when the feed material subjected to this process is in the centimeter (cm) range (eg 10 cm).

  The term “mill” is used in the sense of the present invention when the feed material subjected to this process is in the millimeter (mm) or nanometer (nm) range (eg 10 mm).

  According to another preferred embodiment of the invention, the aqueous solution obtained in step e) or step f) comprising at least one alkaline earth metal bicarbonate is 5 to 130 ° dH, preferably 10 to 60. It has a hardness of ° dH, most preferably 15 to 50 ° dH.

  For the interpretation of the present invention, the hardness refers to German hardness, and is represented by “degrees of German hardness ° dH”. In this regard, hardness refers to the total amount of alkaline earth metal ions in an aqueous solution containing alkaline earth metal bicarbonate, using ethylenediaminetetraacetic acid (EDTA) and Eriochrome T as an equivalent point indicator by complex titration at pH 10. Measured.

  The aqueous solution comprising at least one alkaline earth metal bicarbonate and obtained in step e) or step f) is preferably in the range 6.5 to 9, preferably 6.7 to 7.9 at 20 ° C. And most preferably has a pH in the range of 6.9 to 7.7.

  According to one embodiment of the present invention, the aqueous solution comprising at least one alkaline earth metal bicarbonate and obtained in step e) or step f) is 1 to 700 mg / l as calcium carbonate, preferably Those having a calcium concentration of 50 to 650 mg / l, most preferably 70 to 630 mg / l. According to another embodiment, the aqueous solution comprising at least one alkaline earth metal hydrogen carbonate and obtained in step e) or step f) is 1 to 200 mg / l, preferably 2 to 150 mg, as magnesium carbonate. / L, most preferably having a magnesium concentration of 3 to 125 mg / l.

  According to yet another embodiment of the invention, the aqueous solution comprising at least one alkaline earth metal bicarbonate and obtained in step e) or step f) is lower than 1.0 NTU, preferably less than 0. Those having a turbidity value lower than 5 NTU, most preferably lower than 0.3 NTU.

  At least step d) is preferably carried out at a temperature in the range of 5 to 55 ° C, preferably in the range of 20 to 45 ° C.

According to an even more preferred embodiment of the invention, the aqueous solution obtained in step e) or step f) is:
(X) calcium bicarbonate, preferably calcium bicarbonate having a calcium concentration of 25 to 150 mg / l as calcium carbonate, or (xx) magnesium bicarbonate, preferably carbonate having a magnesium concentration of> 0 to 50 mg / l Magnesium hydrogen or (xxx) a mixture of calcium bicarbonate and magnesium bicarbonate, preferably a mixture having a total calcium and magnesium concentration of 25 to 200 mg / l as calcium carbonate and magnesium carbonate.

According to one most preferred embodiment of the invention, the aqueous solution obtained in step e) or step f) is:
Calcium bicarbonate having a calcium concentration of 45 mg / l as calcium carbonate, or a mixture of calcium bicarbonate and magnesium bicarbonate having a calcium concentration of 80 to 120 mg / l as calcium carbonate and a magnesium concentration of 20 to 30 mg / l as magnesium carbonate Is included.

A mixture of calcium bicarbonate and magnesium bicarbonate can be obtained when dolomite, semi-calcined and / or fully calcined dolomite-containing materials are used as materials containing alkaline earth metal carbonates. In the sense of the present invention, the calcined dolomite contains calcium oxide (CaO) and magnesium oxide (MgO), while the semi-calcined dolomite consists of Mg in the form of magnesium oxide (MgO) and calcium carbonate (CaCO ₃ ). Although it contains the form of Ca, a small amount of some calcium oxide (CaO) may be included.

In a preferred embodiment of the present invention, the method is a continuous process. However, the process of the invention can also be carried out in a semi-batch mode. In this case, the produced suspension S can exhibit a total particle surface, for example, around 1000000 m ² / metric tons and is subjected to the method of the present invention. The product, ie an aqueous solution of alkaline earth metal bicarbonate, is then discharged from the process until the total particle surface indicated by the remaining product suspension S is around 1000 m ² / metric tons, and then at least A new amount of the at least one substance comprising a type of alkaline earth metal carbonate and optionally a small amount of at least one type of alkaline earth metal hydroxide relative to the alkaline earth metal carbonate. Introduce into the process. It should be noted that the total particle surface can be determined by measuring the specific surface area (SSA) of the suspension S and the dry content of the suspension S each time during the continuous process.

  Most preferably, the continuous process is by discharge of an aqueous solution containing at least one alkaline earth metal bicarbonate and a measurement of the solids content of the suspension S, or by complex titration, or by the alkaline earth Controlled by measured conductivity of metal bicarbonate solution.

  In yet another embodiment of the invention, the filtration device of step e) is a membrane filter, such as a microfiltration membrane and / or an ultrafiltration membrane. In a preferred embodiment, the filtration device of step e) is a tubular membrane filter having a pore size of 0.02 μm to 0.5 μm, preferably 0.05 to 0.2 μm. Preference is given to plate-like and / or tube-type filters. The tube-type filter preferably has a tube inner diameter of 0.1 to 10 mm, more preferably 0.1 to 5 mm. In a preferred form, the membrane is made of a sintered material, porous porcelain or synthetic polymer, such as polyethylene, Teflon.

  A further object of the invention is at least obtained by the method of the invention for the production of precipitated alkaline earth metal carbonates and / or hydromagnesite, in particular for the preparation of precipitated calcium carbonate and / or hydromagnesite. Use of an aqueous solution containing one type of alkaline earth metal bicarbonate. Such precipitated alkaline earth metal carbonates, particularly precipitated calcium carbonate and hydromagnesite, are useful as fillers in many industrial applications, for example as paper, paint or plastic fillers.

  Another object of the present invention is the use of an aqueous solution comprising at least one alkaline earth metal hydrogen carbonate obtained by the process of the present invention for the mineralization of water.

  Further objects of the present invention are: I) the step of preparing feed water, II) the step of preparing an aqueous solution containing at least one alkaline earth metal bicarbonate, and III) the feed water of step I) and step II). The mineralization method of water including the process of combining the aqueous solution containing at least 1 type of alkaline-earth metal hydrogencarbonate of this, and obtaining mineralized water.

  According to one embodiment of the water mineralization method, the aqueous solution comprising at least one alkaline earth metal bicarbonate of step II) is at least 3 ° dH than the hardness of the feed water of step I), preferably It has a hardness of at least 5 ° dH.

  According to one preferred embodiment, the aqueous solution comprising at least one alkaline earth metal hydrogen carbonate of step II) has a hardness of at least 15 ° dH.

  According to another embodiment of the water mineralization process, the mineralized water has a calcium concentration of 1 to 700 mg / l, preferably 50 to 650 mg / l, most preferably 70 to 630 mg / l as calcium carbonate. It is. According to yet another embodiment of the water mineralization method, the mineralized water has a magnesium concentration of 1 to 200 mg / l, preferably 2 to 150 mg / l, most preferably 3 to 125 mg / l as magnesium carbonate. Is.

A still further object of the present invention is to
IV) a step of preparing an aqueous solution containing at least one alkaline earth metal hydrogen carbonate, and V) heating the aqueous solution containing at least one alkaline earth metal hydrogen carbonate in step IV) to prepare precipitated alkaline earth. And / or VII) adding at least one alkaline earth metal hydroxide or alkaline earth metal oxide to the solution of step IV) to obtain a precipitated alkaline earth metal carbonate. A method for producing a precipitated alkaline earth metal carbonate comprising a step.

  By heating an aqueous solution containing at least one alkaline earth metal bicarbonate, water evaporates from the solution and at some point alkaline earth metal carbonate begins to precipitate from the solution.

  According to a preferred embodiment of the method for producing a precipitated alkaline earth metal carbonate, the precipitated alkaline earth metal carbonate is an amorphous alkaline earth metal carbonate, such as amorphous calcium carbonate or It is selected from magnesium carbonate, calcite, aragonite or vaterite type crystalline calcium carbonate, magnesite and hydromagnesite, or a mixture of the foregoing.

  “Conductivity” is used in the sense of the present invention as an inverse indicator of how salt-free, ion-free, or impurity-free the water being measured; Becomes lower. Conductivity can be measured with a conductivity meter and is expressed in units: S / m.

  “Grinded calcium carbonate (GCC)” in the sense of the present invention is obtained from natural sources, for example marble, chalk or limestone, and by treatments such as grinding, sieving and / or fractionation (wet and / or Calcium carbonate processed dry (for example by a cyclone).

“Precipitated calcium carbonate (PCC)” means, in the sense of the present invention, generally by precipitation after the reaction of carbon dioxide and lime in an aqueous environment, or by precipitation of a calcium / carbonate source in water, or in solution Is a synthetic material obtained by precipitation of calcium ions and carbonate ions (eg, CaCl ₂ and Na ₂ CO ₃ ). Precipitated calcium carbonate exists in three main crystalline forms: calcite, aragonite and vaterite, each of which has many different polymorphs (crystal habits). Calcite has typical crystals such as canine (S-PCC), rhombohedral (R-PCC), hexagonal columnar, table-like, colloidal (C-PCC), cubic and ridged columnar (P-PCC). It has a trigonal structure with a wrinkle. Aragonite has a variety of varieties, including hexagonal columnar typical crystal habits and thin and elongated ridge columns, curved blades, pointed pyramids, chiseled crystals, branched dendrites and coral or worm-like forms. It has an orthorhombic structure.

Throughout this document, the “particle size” of the calcium carbonate product is indicated by this particle size distribution. The value d _x represents the diameter where x weight percent of the particles have a diameter less than d _x . This means that the d ₂₀ value is the particle size at which 20% by weight of the total particles are smaller than this value, and the d ₇₅ value is the particle size at which 75% by weight of all the particles are smaller than this value. . Therefore, d ₅₀ value is the weight median particle size, i.e., 50 wt% of the total particles greater than this particle size, or smaller. For the interpretation of the present invention, the particle size is indicated by the weight median particle size d ₅₀ unless otherwise specified. This value was measured using a Mastersizer 2000 device manufactured by Malvern Instruments GmbH (Germany).

  The term “mineralization”, as used in the present invention, increases the essential mineral ions in water that contains no mineral or insufficient amount of mineral to obtain palatable water. It means to make it. Mineralization can be performed by adding at least calcium carbonate to the water to be treated. In some cases, for example, for further health-related benefits or to ensure proper uptake of some other essential mineral ions and trace elements, additional materials are mixed with calcium carbonate and then remineralized It may be added to water during the process. According to national guidelines on human health and drinking water quality, remineralization products may contain additional minerals such as magnesium, potassium or sodium, such as magnesium carbonate, magnesium sulfate, potassium bicarbonate, sodium bicarbonate or essential Other minerals containing trace elements may be included.

  Substances useful for use in the method of the present invention for preparing an aqueous solution comprising at least one alkaline earth metal bicarbonate are natural inorganic substances or salts containing calcium carbonate and / or magnesium, or Synthetic inorganic substances or salts containing calcium carbonate and / or magnesium.

  Useful naturally occurring inorganic substances are, for example, marble, limestone, chalk, dolomite marble and / or dolomite. Synthetic substances are, for example, precipitated calcium carbonate in calcite, aragonite and / or vaterite crystalline form. However, naturally occurring inorganic substances are preferred because they inherently contain some essential trace elements.

  “Turbidity”, in the sense of the present invention, is caused by individual particles (suspended solids) and generally indicates a haze or haze of fluid that is not visible to the naked eye. Turbidity measurement is a key water quality test and can be performed with a turbidimetric meter. The unit of turbidity measured by the calibrated nephelometer used in the present invention is shown as neferometry turbidity unit (NTU).

The process of the present invention for the preparation of an aqueous solution comprising at least one alkaline earth metal bicarbonate comprises
a) preparing water;
b) providing at least one substance comprising at least one alkaline earth metal carbonate and optionally a small amount of at least one alkaline earth metal hydroxide relative to the alkaline earth metal carbonate, The at least one substance is in dry or aqueous form, step c) providing CO ₂ ;
d) (i) the water of step a), at least one substance comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide of step b), and step c) with CO ₂ , or (ii) the water of step a) and at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide of step b). Combined with at least one material comprising, obtaining an alkaline aqueous suspension of at least one material comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide Either subsequently combining the alkaline aqueous suspension with the CO _{2 of} step c) to obtain a product suspension S having a pH of 6 to 9, wherein the product suspension The suspension S contains particles, a process,
e) A step of filtering at least a part of the product suspension S by passing at least a part of the product suspension S through a filtration device to obtain an aqueous solution containing at least one alkaline earth metal hydrogen carbonate. ,
f) a step of subjecting at least a part of the particles of the generated suspension S to a particle fragmentation step,
Here, step f) can be carried out before and / or in parallel with and / or after step e),
Here, the particles of the product suspension S obtained in step d) exhibit a total particle surface area (SSA _total ) of at least 1000 m ² / product suspension S metric tons,
However, the addition of CO _{2 in} step c) is prior to the addition of at least one substance comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide in step b). It is a method on condition that it is not performed.

  The process according to the invention is preferably carried out in a reactor system provided with at least a tank, at least one filtration device and means for connecting the tank to the at least one filtration device, for example pipes or tubes. The reactor system may also be equipped with measuring equipment, such as a unit for measuring pressure, temperature, pH, turbidity.

1 illustrates one embodiment of the present invention in which a filtration device and a grinding device are arranged in a series or in-line arrangement. 6 illustrates another embodiment of the present invention. 6 illustrates another embodiment of the present invention.

  The tank is fitted with a stirrer, water, carbon dioxide and at least one supply port for a substance comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide. It has been. There is also a filtration device connected to the tank, where a pH of 6 to 9 prepared in the tank is obtained in order to obtain an aqueous solution containing at least one alkaline earth metal bicarbonate. Pass at least a portion of the resulting suspension S.

  In addition, the reactor system includes a fragmentation device (particle size reduction device) that is assembled in a parallel or series arrangement with respect to the filtration device or introduced into the vessel. The vessel is connected to a grinding and / or grinding device, where at least some of the particles contained in the product suspension S are subjected to particle size reduction. The grinding and / or grinding device is arranged in such a way that only a part of the product suspension S contained in the tank is circulated back into the tank after passing through the grinding and / or grinding device. ("Parallel arrangement"), all the product suspension S that is placed in-line with the filtration device and passes through the grinding and / or grinding device is then filtered in the filtration device. It may be. The filtration device may also be placed in-line before the grinding and / or grinding device (“in-line or in series”). When the grinding and / or grinding device is introduced into the vessel, part or all of the product suspension S is passed through the grinding and / or grinding device.

  Preferably, at least a portion of the solution that has passed through the filtration device is collected to obtain an aqueous solution containing at least one alkaline earth metal bicarbonate. However, if the measured turbidity value of the aqueous solution containing at least one alkaline earth metal bicarbonate discharged from the filtration device is found to be above 1.0 NTU, the at least one alkaline earth An aqueous solution containing an organometallic bicarbonate is recirculated into the reactor.

  The water that can be used in the method of the present invention can be derived from various sources. The water preferably treated by the method of the present invention is desalinated seawater, brackish water or brine, treated wastewater or natural water, such as groundwater, surface water or rainwater.

  According to another exemplary embodiment of the present invention, sea water or brackish water is first pumped from the ocean by an open water intake or underground intake (such as a well) and then physical pretreatment, eg, sieving. Perform the sediment or sand removal process. Depending on the water quality required, further processing steps such as agglomeration and flocculation may be required to reduce the likelihood of fouling on the membrane. The pretreated seawater or brackish water can then be distilled using, for example, multistage flash distillation, multiple effect distillation or membrane filtration (such as ultrafiltration or reverse osmosis) to remove residual particulates and dissolved materials.

A flow control valve or other means may be used for control of the flow rate of carbon dioxide into the stream. For example, a CO ₂ input block and a CO _{2 in-} line metering device can be used for control of the rate of CO ₂ flow. According to an exemplary embodiment of the present invention, CO ₂ is, CO ₂ feeding unit, is injected using a combined unit comprising a static mixer and inline CO ₂ metering device.

  The amount of carbon dioxide input is preferably controlled by the pH of the aqueous alkaline earth metal bicarbonate solution produced.

  The alkaline aqueous suspension formed in the reactor system is in the range of 0.1 to 80% by weight, preferably in the range of 3 to 50% by weight, more preferably in relation to the total weight of the product suspension S. It has a solids content in the range of 5 to 35% by weight.

The substance containing at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide introduced into the tank may be in a dry or aqueous form. Preferably, the substance comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide has a range of 0.1 μm to 1 mm, preferably 0.7 μm to 100 μm. It has a weight-weighted median particle size (d ₅₀ ). According to one embodiment of the invention, the substance comprising at least one alkaline earth metal carbonate is preferably ground calcium carbonate (GCC), such as marble, limestone or chalk; or dolomite.

  According to another embodiment of the invention, the material comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide is 0 Those having an HCl insoluble content of 0.02 to 90% by weight, preferably 0.05 to 7% by weight. The HCl insoluble content can be, for example, minerals such as quartz, silicates, mica and / or pyrite.

  According to yet another embodiment of the invention, at least one alkaline earth metal carbonate and optionally a small amount of at least one alkaline earth metal hydroxide relative to the alkaline earth metal carbonate. An aqueous suspension of at least one substance comprises water and at least one alkaline earth metal carbonate and optionally a small amount of at least one alkaline earth metal hydroxide relative to the alkaline earth metal carbonate. It is newly prepared by mixing a substance containing An on-site preparation of the aqueous suspension would be preferred. Because it is premixed, the aqueous suspension may require the addition of additional agents (such as stabilizers or biocides) that may be unwanted compounds in the remineralized water. Because. According to one preferred embodiment of the invention, the time interval between the preparation of the aqueous suspension and the injection of the aqueous suspension is sufficient to avoid bacterial growth in the aqueous suspension. short. According to one exemplary embodiment, the time interval between preparation of the aqueous suspension and injection of the aqueous suspension is less than 48 hours, less than 24 hours, less than 12 hours, less than 5 hours, less than 2 hours. Or less than 1 hour. According to another embodiment of the invention, the injected aqueous suspension meets the microbiological quality requirements specified in the national guidelines for drinking water.

  An aqueous suspension comprising at least one alkaline earth metal carbonate and optionally at least one substance comprising a small amount of at least one alkaline earth metal hydroxide relative to the alkaline earth metal carbonate. Can be prepared using, for example, a mixer such as a mechanical stirrer for dilute slurries, or a specific powder-liquid mixing device for more concentrated slurries. Depending on the concentration of the aqueous suspension to be prepared, the mixing time can be 0.5 to 30 minutes, 1 to 20 minutes, 2 to 10 minutes, or 3 to 5 minutes. According to one embodiment of the invention, the aqueous suspension is prepared using a mixing device, wherein the mixing device is capable of mixing and charging the aqueous suspension at the same time.

  The water used to prepare the aqueous suspension can be, for example, distilled water, feed water or industrial water. According to one preferred embodiment of the invention, the water used to prepare the aqueous suspension is feed water, for example a permeate or a distillate obtained in the desalination process.

  According to one embodiment, an aqueous solution comprising at least one alkaline earth metal bicarbonate is injected directly into the feed stream. For example, a clear solution containing alkaline earth metal bicarbonate can be injected into the feed stream at a rate controlled by continuous conductivity measurements.

  According to one embodiment, the predetermined parameter value is a pH value, where the pH value is 6.5 to 9, preferably 7 to 8.

  1 and 2 are intended to illustrate the method according to the invention.

FIG. 1 illustrates one embodiment of the present invention in which a filtration device and a grinding device are arranged in a series or in-line arrangement. The process according to the invention preferably comprises a tank (1) fitted with a stirrer (2), water, carbon dioxide and at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal water. It is carried out in a reactor system provided with at least one feed port (not shown) for at least a substance comprising oxide and a pH measuring device (not shown). At least one substance comprising at least one alkaline earth metal carbonate and optionally a small amount of at least one alkaline earth metal hydroxide relative to the alkaline earth metal carbonate is in a dry form in the vessel. Or it can be introduced either in aqueous form. Connected to the reactor is at least one filtration device (4) having an outlet for an aqueous solution comprising the at least one alkaline earth metal bicarbonate. If more than one filtration device is present, they can be arranged either in parallel, or in-line (in series), or in a parallel / in-line manner. The filtration device (4) is preferably a membrane filter. The grinding device (18) is placed after the filtration device (4) and is also connected to the tank (1). At least one substance (6) comprising at least one alkaline earth metal carbonate and optionally a small amount of at least one alkaline earth metal hydroxide relative to the alkaline earth metal carbonate, water ( 14) and CO ₂ are introduced into the tank (1) from at least one feed port (not shown) and stirred with a stirrer (2) to obtain a product suspension S having a pH of 6 to 9 The The product suspension S is then fed to the filtration device (4) (8), where all coarse particles, ie particles having a size of at least 0.2 μm contained in the suspension, are filtered. (4) is held within. At least a portion of the suspension discharged from the filtration device (4) is fed into the grinding device (18) from where it is recirculated back into the tank (1). At least a portion of the clear aqueous solution containing at least one alkaline earth metal bicarbonate is discharged (10) from the filtration device (4).

In this embodiment, CO ₂ (20) is preferably fed into the reactor system before the grinding device (18) but after the filtration device (4). The grinding process continuously produces a fresh and thus active surface of the material comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide. This provides the benefit of increasing the (chemical) reaction rate of the process of the present invention. This process step also reduces the size of the particles of the substance of step c) comprising an alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide, so that the process is sustained. Implementation becomes possible. The flow rate of the suspension S passing through the filtration device (4) is at least 1 m / sec, preferably in the range 1.5 to 10 m / sec, most preferably in the range 3 to 6 m / sec. The flow rate of the suspension S passing through the grinding device is 0.01 to 6 m / sec, preferably 0.1 to 0.5 m / sec.

  Optionally, further treatment (16), eg mechanical treatment or biocide or other, to change the pH of the solution (eg addition of a base such as NaOH), the conductivity of the solution, or the hardness of the solution An additive may be added. As a further option, a clear aqueous solution comprising at least one alkaline earth metal bicarbonate discharged from the filtration device may be diluted with additional water (14). Coarse particles contained in the suspension retained in the filtration device may optionally be recycled to the reactor to make it available for further conversion.

FIG. 2 illustrates another embodiment of the present invention. The method of this embodiment differs from that of FIG. 1 in that the grinding device (18) is placed in parallel with the filtration device rather than after the filtration device. The grinding device (18) is connected to the tank (1) in such a way that the contents of the grinding device (18) can be recycled to the tank (1). Part of the product suspension S having a pH of 6 to 9 is fed to the filtration device (8), while another part of the product suspension S having a pH of 6 to 9 is fed to the grinding device (18 ). In this embodiment, CO ₂ (22) is preferably fed into the reactor system before the grinding device (18). The milled product aqueous suspension S is then circulated (24) from the milling device (18) and returned to the tank (1). This grinding step continuously produces a fresh and thus active surface of the material comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide. Provides the benefit of increasing the (chemical) reaction rate of the process of the invention. This process step also reduces the size of the particles of the substance of step c) comprising an alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide, so that the process is sustained. Implementation becomes possible. The flow rate of the suspension S passing through the filtration device (4) is at least 1 m / sec, preferably in the range 1.5 to 10 m / sec, most preferably in the range 3 to 6 m / sec. The flow rate of the suspension S passing through the grinding device is 0.01 to 6 m / sec, preferably 0.1 to 0.5 m / sec.

FIG. 3 illustrates another embodiment of the present invention. The method of this embodiment differs from that of FIGS. 1 and 2 in that the grinding device (18) consists of grinding beads (3) placed in the tank (1). Connected to the reactor is at least one filtration device (4), which has an outlet for an aqueous solution comprising at least one alkaline earth metal bicarbonate. If more than one filtration device is present, they can be arranged in either parallel or in-line (series) or parallel / in-line fashion. The filtration device (4) is preferably a membrane filter. The filtration device (4) is connected to the tank (1) in such a way that, if necessary, a part of the suspension can be recirculated from the filtration device (4) into the tank (1). . At least one substance comprising at least one alkaline earth metal carbonate (6) and optionally a small amount of at least one alkaline earth metal hydroxide relative to the alkaline earth metal carbonate, water ( 14) and CO ₂ are introduced into the tank (1) from at least one feed port (not shown) and stirred with a stirrer (2) to obtain a product suspension S having a pH of 6 to 9 Is done. In this embodiment, some or all of the particles of the product suspension S are ground by the grinding beads (3) encapsulated in the bath. The product suspension S is then fed to the filtration device (4) (8), where all coarse particles, ie particles having a size of at least 0.2 μm contained in the suspension, are all filtered. ) And a clear aqueous solution containing at least one alkaline earth metal bicarbonate is obtained. At least a portion of the clear aqueous solution containing at least one alkaline earth metal bicarbonate is discharged (10) from the filtration device (4).

  Optionally, further treatment (16), eg mechanical treatment or biocide or other, to change the pH of the solution (eg addition of a base such as NaOH), the conductivity of the solution, or the hardness of the solution An additive may be added. As a further option, a clear aqueous solution comprising at least one alkaline earth metal bicarbonate discharged from the filtration device may be diluted with additional water (14). Coarse particles contained in the suspension retained in the filtration device may optionally be recycled (12) to the reactor to be available for further conversion.

According to one embodiment, the feed water flow rate is 20000 to 500000 m ³ per day.

  The method of the present invention is for producing drinking water, recreational water (such as swimming pool water), industrial water for processing applications, irrigation water, or water for the production of purified alkaline earth metal carbonates. Can be used.

According to one embodiment, the alkaline earth metal hydrogen carbonate solution obtained by the process of the present invention, from 700 mg / l 1 as CaCO _3, preferably 650 mg / l from 50 as CaCO _3, and most preferably as CaCO ₃ It has a calcium concentration of 70 to 630 mg / l. When the slurry further contains a magnesium salt (such as magnesium hydrogen carbonate or magnesium sulfate), the alkaline earth metal hydrogen carbonate solution obtained by the method of the present invention is 1 to 200 mg / l as magnesium carbonate, preferably It may have a magnesium concentration of 2 to 150 mg / l, most preferably 3 to 125 mg / l.

  According to one embodiment of the invention, the alkaline earth metal bicarbonate solution is one having a turbidity lower than 1.0 NTU, preferably lower than 0.3 NTU.

Specific surface area of materials (SSA)
Specific surface area (SSA) was measured using a Malvern Mastersizer 2000 (based on Fraunhofer equation).

Particle size distribution (<% by weight of particles with diameter X) and weight median diameter (d ₅₀ )
The weight median particle diameter and particle diameter mass distribution of the particulate material were determined using a Malvern Mastersizer 2000 (based on Fraunhofer equation).

PH of aqueous suspension
The pH was measured using a Mettler-Toledo pH meter. Calibration of the pH electrode was performed using standard solutions with pH values of 4.01, 7.00, and 9.21.

Solid content of aqueous suspension The solid content of the suspension (also known as “dry weight”) was measured using the Moisture Analyzer HR73 manufactured by Mettler-Toledo (Switzerland) Setting: measured at a temperature of 120 ° C., automatic switch-off 3, standard drying, 5 to 20 g suspension.

Turbidity Turbidity was measured with a Hach Range 2100AN IS Laboratory Turbidimeter and calibration was performed using <0.1, 20, 200, 1000, 4000 and 7500 NTU StabCal turbidity standards (formazin standards). .

Measurement of hardness (German hardness; expressed in “° dH”) Hardness refers to the total amount of alkaline earth metal ions in an aqueous solution containing alkaline earth metal hydrogen carbonate. By complex titration, ethylenediaminetetraacetic acid (EDTA; trademark) The name Titriplex III) is measured using Eriochrome T as the equivalence point indicator.

EDTA (chelating agent) forms soluble and stable chelate complexes with the ions Ca ²⁺ and Mg ²⁺ . 2 ml of 25% ammonia solution, ammonia / ammonium acetate buffer (pH 10) and eriochrome black T indicator were added to 100 ml of the water sample to be tested. Indicators and buffers are usually available as so-called “indicator-buffer tablets”. The indicator forms a red complex with Ca ²⁺ and Mg ²⁺ ions when masked with a yellow dye. At the end of the titration (which is when all the ions are bound to the chelator), the remaining Eriochrome Black T indicator is in free form and shows a green color. If the indicator is not masked, the color changes from magenta to blue. Total hardness can be calculated from the amount of EDTA used.

  The table below shows the conversion of water hardness to various units.

  The carbon dioxide used in the examples is commercially available as “Kohlendioxid 3.0” from PanGas (Dagmelseelen, Switzerland). The purity was ≧ 99.9 Vol%.

Example
Examples of prior art prepared examples of the prior art in the following manner, show different slurries having calcium carbonate at various concentrations, the slurry was prepared from different carbonate rocks were charged batchwise to the supply water.

Feed water was obtained by reverse osmosis desalination and acidified with about 50 mg / l CO ₂ . The slurry was prepared by mixing an appropriate amount of calcium carbonate with 100 ml of feed water using a magnetic stirrer at room temperature, stirring was 1000 to 1500 rpm, and mixing time was 3 to 5 minutes.

Remineralization is performed by adding a small amount of slurry to about 1 liter of acidified feed water, where the slurry and feed water are mixed using a magnetic stirrer, stirring is 1000 to 1500 rpm, mixing The time was 2 minutes. After each addition of the slurry, a sample was taken from the treated feed water and the alkalinity, turbidity, conductivity, pH, and temperature were controlled. A final calcium concentration of 125 mg / l as CaCO ₃ was selected as the target value for remineralization of the feed water. 125 mg CaCO ₃ / l represents a concentration of 0.0125% by weight. For each sample, turbidity of remineralized water was measured immediately after mixing and after a settling period of at least 60 minutes. The turbidity measurement on the sedimented sample was performed to observe the effect of sedimentation in the remineralization method.

  Turbidity was measured with a Hach Range 2100AN IS Laboratory Turbidimeter and calibration was performed using <0.1, 20, 200, 1000, 4000 and 7500 NTU StabCal turbidity standards (formazin standards).

  Total alkalinity was measured with a Mettler-Toledo T70 Titrator using the associated LabX Light Titration software. In this titration, a DGi111-SG pH electrode was used according to the corresponding Mettler-Toledo method M415 of the application broach 37 (water quality analysis). Calibration of the pH electrode was performed using Mettler-Toledo standards with pH values of 4.01, 7.00 and 9.21.

[Example 1]
Slurry A
Two types of slurries with calcium carbonate concentrations of 0.5 and 5% by weight based on the total weight of the slurry were mixed with a medium particle size of 3.5 μm and 0.2% by weight of HCl insoluble with respect to the total weight of calcium carbonate Prepared from finely divided calcium carbonate from marble with a content (Salses, France).

The results summarized in Table 1, in the remineralization process using 0.5 wt% and 5 wt% of CaCO ₃ slurry, both show similar turbidity values. After the settling period, the sample showed a turbidity value lower than 0.5 NTU.

[Example 2]
Slurry B
Three types of slurries with calcium carbonate concentrations of 0.5, 1 and 10% by weight with respect to the total weight of the slurry were 2.8 μm medium particle size and 1.5% by weight HCl with respect to the total weight of calcium carbonate. Prepared from finely divided calcium carbonate from marble (Bathast, Australia) having an insoluble content.

  The results summarized in Table 1 show similar turbidity values for all three remineralization methods. However, the turbidity values measured in sedimented samples taken after 2 minutes of remineralization are higher than those in Example 1, which may be due to the difference in the HCl insoluble content of the marble calcium carbonate.

[Example 3]
Slurry C
A slurry having a calcium carbonate concentration of 5% by weight with respect to the total weight of the slurry is obtained with a medium particle size of 3 μm, a specific surface area (SSA) of 2.6 m ² / g and 0.1% by weight with respect to the total weight of calcium carbonate Prepared from finely divided calcium carbonate from limestone (Orgon, France) with a HCl insoluble content of

  The results summarized in Table 1 indicate that the turbidity values measured in the sedimentation samples are much lower than those in Examples 1 and 2, which may be due to differences in carbonate rock geological structure.

  The results summarized in Table 1 show high turbidity in freshly prepared samples and most samples even after settling.

[Example 4]
Three types of slurries having a calcium carbonate concentration of 5% by weight with respect to the total weight of the various particle size slurries were 0.2% by weight based on the particle size of 3.5, 9 and 20 μm and the total weight of calcium carbonate, respectively Was prepared from finely divided calcium carbonate derived from marble having a HCl insoluble content of

  The results summarized in Table 2 show that after the settling period, the turbidity of water remineralized at a large particle size, ie 20 μm, is low compared to the turbidity of water remineralized at a small particle size, ie 3.5 μm. It shows that it has a turbidity value, which is logic due to the fact that coarse particles settle much faster than fine particles.

  The results summarized in Table 2 show the large turbidity of freshly prepared samples. After the settling period, the water remineralized with a large particle size, ie 20 μm, shows a lower turbidity value than the water remineralized with a small particle size, ie 3.5 μm, which means that coarse particles are fine particles. This is due to the fact that it settles much faster than it does, but as soon as the sample is shaken, the turbidity of the sample increases.

Marble calcium carbonate with a weight median diameter (d ₅₀ ) of 3.5 μm is approximately 2.61 m ² / g corresponding to a suspension metric tons of 326.3 m ² /0.0125 wt% solids. The total particle surface is shown.

Marble calcium carbonate having a weight median diameter (d ₅₀ ) of 9 μm is approximately 1.75 m ² / g total equivalent to 218.8 m ² /0.0125 wt% solids suspension metric tonnes. The particle surface is shown.

Marble calcium carbonate having a weight median diameter (d ₅₀ ) of 20 μm is approximately 0.94 m ² / g total, corresponding to a metric ton of suspension of 117.5 m ² /0.0125 wt% solids. The particle surface is shown.

  From the above information, it can be deduced that the dissolution rate of calcium carbonate is reduced by reducing the specific surface area of the calcium carbonate particles present in the suspension.

Examples relating to the invention Process diagrams of the general method of the method according to the invention are shown in FIGS.

The feed water used in the examples of the present invention was obtained from the ion exchange facility Type Elite 1BTH of Christ (Eiche, Switzerland), and the feed water had the following water quality standards after ion exchange:
Sodium 169mg / l
Calcium 2mg / l
Magnesium <1mg / l
° dH 0.3

  To illustrate the method according to the present invention, the following different method routes were used:

Method A
The reactor suspension is passed through a mill in which milling beads are present.

[Example 5]
Microdol A extra (dolomite)
In this example, dolomite Microdol A extra obtained from Norwegian Talc (Knarrevik) was used as at least one alkaline earth metal carbonate. Reactions and working conditions are shown in Tables 3 and 4.

  Method A, 25 ° C. (bath temperature)

The total mineral surface of the particles in the suspension of this test is 427500 m ² / metric ton of suspension.

  Method A, 40 ° C (bath temperature)

The total mineral surface of the particles in the suspension of this test is 167428 m ² / metric ton of suspension.

The ratio of moles of CaCO ₃ produced to the moles of CO ₂ used in this example is 1: 0.54.

[Example 6]
Marble In this example, marble sold under the trade name “Omycarb 10 AV” from Omya International (Switzerland) was used as the alkaline earth metal carbonate. The HCL insoluble content was 0.7% by weight. Reactions and working conditions are shown in Table 5.

  Method A, 24 ° C (bath temperature)

The total mineral surface of the particles in the suspension of this test is 421500 m ² / metric ton of suspension.

The ratio of moles of CaCO ₃ produced to the moles of CO ₂ used in this example is 1: 0.45.

Use of an aqueous solution containing calcium bicarbonate for the preparation of precipitated calcium carbonate 2 liters of a clear permeate obtained according to method B of this example was heated at 70 ° C. for 2 hours, and the resulting precipitate was 0.2 μm And collected by filtration using a membrane filter having a pore size of.

XRD analysis of the product precipitate shows the following:
Aragonite type precipitated calcium carbonate (PCC) 85.8 wt%
Magnesium-rich calcite-type precipitated calcium carbonate 14.2% by weight
Silica / silicate <0.1% by weight

  Thus, XRD results indicate that very clean precipitated calcium carbonate can be prepared from silicate-mixed feedstock.

[Example 7]
Marble / silicate blend, Austria In this example, marble / silicate blend (Omyacarb 10 AV "from Omya International (Switzerland), mix with 7% mica from Aspanger Kaolin (Austria)) is used as starting material The HCL insoluble content was 7.5% by weight (mainly mica), and the reaction and working conditions are shown in Table 6.

  Method A, 24 ° C (bath temperature)

The total mineral surface of the particles in the suspension of this test is 153500 m ² / metric ton of suspension.

The ratio of moles of CaCO ₃ produced to the moles of CO ₂ used in this example is 1: 1.66.

  This example clearly shows that the present invention can also be practiced with a high amount of impurities (in this case, the impurities are mica). This is a cost-effective alternative to methods where only pure starting products can be used and this may have to be transported from a distance to the production site.

Use of an aqueous solution containing calcium bicarbonate for the preparation of precipitated calcium carbonate 2 liters of a clear permeate obtained according to method B of this example was heated at 70 ° C. for 2 hours, and the resulting precipitate was 0.2 μm And collected by filtration using a membrane filter having a pore size of.

XRD analysis of the product precipitate shows the following:
Aragonite PCC 97.3% by weight
Magnesium-rich calcite PCC 2.7% by weight
Silica / silicate <0.1% by weight

  Thus, the XRD results show that very clean precipitated calcium carbonate is obtained from the starting product with an insoluble content (impurities) of 7.5% by weight.

[Example 8]
Semi-calcined Dolomite Method A = Pass through a mill with ground beads in the mill, T = 20 ° C.
Ground and partially calcined German dolomite (with an average particle size of 7.5 μm and a specific surface area (SSA) of 0.90 m ² / g, manufactured by Dolomitwerk Jettenberg, Schondorfer GmbH (Oberjettenberg)) 2% by weight solid content in a Christ ion exchange equipment). The resulting suspension had a conductivity of 1104 μS / cm.

This suspension is pumped from the reactor in a circulating manner at a rate of 2200 l / h and a temperature of 20 ° C. and passed through three membrane modules (Microdyn-Mod MD 063 TP 2N) of 0.2 m ² each. And pumped back into the reactor. The membrane modules were arranged in a line in series.

  Samples were taken from the suspension every 15 minutes and the conductivity, German hardness and pH of the samples were measured. Table 7 shows the results obtained.

  Table 7 shows a stable state for pH and conductivity below 9.5 after 3 to 3.5 hours.

  Table 8 shows the results of ion chromatography (882 Compact IC Plus, Metrohm) of samples taken after 15, 90, 120, 195 and 285 minutes.

  Table 8 also shows a stable state with respect to the magnesium content after 3 to 3.5 hours.

Table 9 shows the reaction conditions used and the pH, hardness, d ₁₀ , d ₅₀ , d ₉₀ and specific surface area (SSA) of samples taken after ₁₅ , ₉₀ , 120, 195 and 285 minutes. The sample was collected in a tank, and the pH value of the permeate was measured by titration.

At the start, the total particle surface of the suspension in this test was measured to be 15912 m ² / metric ton of suspension and the medium diameter (d ₅₀ ) was 7.5 μm. After 195 minutes, the median diameter (d ₅₀ ) was measured to be 0.74 μm and the total particle surface of the suspension was 126000 m ² / metric ton of suspension.

2 liters of clear permeate sampled 285 minutes after use of aqueous solution containing calcium bicarbonate for preparation of precipitated calcium carbonate was heated at 70 ° C. for 2 hours, and the resulting precipitate (P) was 0.2 μm Were collected by filtration using a membrane filter having a pore size of and analyzed by XRD. The filtrate was evaporated to dryness and the residue (R) was analyzed by XRD.

  XRD analysis of the product precipitate as well as the resulting residue shows the following:

[Example 9]
PCC Langenau In this test, precipitated calcium carbonate (PCC) was used.

This PCC was made by adding a 0.1 wt% solution of portlandite to 25 ° dH tap water to raise the pH of the water from pH 6.4 to pH 7.8. The precipitated CaCO ₃ obtained in this way was used for this test.

  Method A, 20 ° C (bath temperature)

The total mineral surface of the particles in the suspension of this test is 71400 m ² / metric ton of suspension.

The ratio of moles of CaCO ₃ produced to the moles of CO ₂ used in this example is 1: 3.38.

[Example 10]
Dolomite / limestone blend
Pilot Plant Test In this example, 1 part of Microdol A extra (dolomite described in Example 5) was mixed with 2 parts of limestone from the Avignon region (France) and used as an alkaline earth metal carbonate blend.

  The purpose of the test of Example 10 was to make a solution of alkaline earth metal bicarbonate at a pH of 6.5 to 6.7 on a pilot scale.

This alkaline earth metal carbonate blend had a d _{10 of} 0.43 μm, a d ₅₀ of 2.43 μm and a d ₉₀ of 6.63 μm at the start of the test.

  This blend was fed as a 50 wt% suspension in water.

  The reaction and working conditions are shown below.

Method A = Pass through a mill with grinding beads in the mill, bath temperature T = 18.5 ° C.
Supply tank volume: 1.0 m ³
Supply water: Deionized water obtained from an ion exchange facility in Christ (Esch, Switzerland) (<1 mg / l for alkaline earth metal carbonate)
8.0m ² , inner diameter 5.5mm, 3m long, 174 parallel tube cross-flow polyethylene membrane module (Seprodin filter module SE 150 TP 1L / DF, Microdyn)
Pore diameter 1.0μm
Supply flow rate of the suspension S to the crossflow membrane unit: 36 m ³ / hour, membrane passage speed: 3 m / second Pressure at the supply port of the crossflow membrane: 1 bar Pressure at the discharge port of the crossflow membrane: 0.3 bar Pressure at the solution outlet: 0.05 bar Supply flow rate of the suspension S to the fragmentation device: 0.40 m ³ / hour Pressure at the supply port of the mill: 0.7 to 0.8 bar CO ₂ input: 1.0 L / min at a pressure of 1.5 to 1.6 bar Suspension S feed solids content: 15% by weight

Results measured for 44 hours of continuous operation:

The specific particle surface of Suspension S obtained according to the method of the present invention and collected 44 hours later was 408000 m ² / S metric tonnes of suspension.

A first tap water with 45 mg / l alkaline earth metal carbonate (total of CaCO ₃ / MgCO ₃ ) was made by diluting the permeate of this test with the feed water. The production capacity of this test corresponds to approximately 6.7 m ³ / hour at an alkaline earth metal carbonate concentration of 45 mg / l.

A tap water of a second water quality containing 100 mg / l alkaline earth metal carbonate 1 (CaCO ₃ ) and 10 to 15 mg / l alkaline earth metal carbonate 2 (MgCO ₃ ) was used as the permeate for this test. Prepared by diluting with feed water. The production capacity of this test corresponds to approximately 2.7 m ³ / hr at concentrations of 100 mg / l CaCO ₃ and 10 to 15 mg / l MgCO ₃ .

[Example 11]
Further Pilot Plant Test This example shows a further test for the preparation of an aqueous solution of calcium bicarbonate on a pilot scale. The resulting calcium bicarbonate solution is then used for soft water remineralization. Soft water can be, for example, natural soft water from ground water or surface water sources, desalinated water by reverse osmosis or distillation, rainwater. The test was performed using different calcium carbonate products as raw materials for the preparation of a calcium carbonate suspension (hereinafter referred to as slurry), and a resulting calcium bicarbonate solution was obtained after carbon dioxide was charged.

  Table 10 below summarizes the properties of the calcium carbonate used during the remineralization pilot test with an initial slurry volume of 1200 L.

  Table 11 below summarizes the properties of the calcium carbonate product slurry used in this test.

  The calcium carbonate suspension (or “slurry”) listed in Table 11 was prepared by mixing micronized calcium carbonate powder and reverse osmosis water (RO water). RO water was generated on-site using a reverse osmosis unit and had standard water quality as outlined in Table 12 below.

  The tank was completely filled with the respective calcium carbonate suspension. The calcium carbonate suspension was then pumped from the tank to the mill and from here to a membrane filtration device for filtration. The mill was used as the input point for carbon dioxide required for dissolution of calcium carbonate in water. The resulting dissolved bicarbonate was then passed through the membrane, while undissolved calcium carbonate was fed back into the bath. Of the various water parameters, conductivity was used as a surrogate for measuring the amount of dissolved bicarbonate obtained by this method.

  The conditions for carbon dioxide and calcium carbonate input can be inferred from Table 13.

  Table 14 below shows the results obtained at the end of tests 1 and 2 (6 to 7 hours per day) of the test of slurry 2 (with a slurry having a solid content of 2 wt% sample A) Summarize.

The results shown in Table 15 were obtained using the slurry 1: about 10% by weight of sample A. The test was performed using the same CO ₂ input ratio of 0.3 L CO ₂ / L concentrate, and the results showed the values obtained at the end of all test days.

Effect of CO ₂ excess ratio In addition to the surface area of solids present in the slurry, the stoichiometric ratio of carbon dioxide to calcium carbonate, ie the measured value as CO ₂ flow rate / concentrate flow rate, is also It is expected to affect the dissolution of calcium carbonate in water. Thus, the final concentration of dissolved bicarbonate, measured as the final conductivity, should increase proportionally to the CO ₂ charged in stoichiometric excess into the slurry. The results shown in Table 16 were both performed using two types of slurries made with sample A (d ₅₀ = 13.7 μm, SSA = 1.3 m ² / g). High solids content (slurry 1: about 10% by weight) and slurry 2 was initially low solids content (slurry 2: about 2%. The flow rate of carbon dioxide and concentrate was the target chemistry. The CO ₂ flow rate ratio of 0.12, 0.3 and 0.6 (L CO ₂ / L concentrate), where the stoichiometric CO ₂ / CaCO ₃ ratio is 1 time, 2.5 times and 5 times respectively. Adjusted to be achieved.

The results of this series of tests show that the conductivity increases proportionally to the target stoichiometric CO ₂ / CaCO ₃ ratio measured as an L CO ₂ / L concentrate.

Claims (28)

A method for preparing an aqueous solution comprising at least one alkaline earth metal bicarbonate,
a) preparing water;
b) providing at least one substance comprising at least one alkaline earth metal carbonate and optionally a small amount of at least one alkaline earth metal hydroxide relative to the alkaline earth metal carbonate, The at least one substance is in dry or aqueous form, step c) providing CO ₂ ;
d) (i) the water of step a), at least one substance comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide of step b), and step c) with CO ₂ , or (ii) the water of step a) and at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide of step b). Combined with at least one material comprising, obtaining an alkaline aqueous suspension of at least one material comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide Either subsequently combining the alkaline aqueous suspension with the CO _{2 of} step c) to obtain a product suspension S having a pH of 6 to 9, wherein the product suspension The suspension S contains particles, a process,
e) A step of filtering at least a part of the product suspension S by passing at least a part of the product suspension S through a filtration device to obtain an aqueous solution containing at least one alkaline earth metal hydrogen carbonate. ,
f) a step of subjecting at least part or all of the particles of the generated suspension S to a particle fragmentation step,
Here, step f) can be carried out before and / or in parallel with and / or after step e),
Here, the particles of the product suspension S obtained in step d) exhibit a total particle surface area (SSA _total ) of at least 1000 m ² / product suspension S metric tons,
However, the addition of CO _{2 in} step c) is prior to the addition of at least one substance comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide in step b). On condition that not
Method. 2. The process according to claim 1, wherein the particles of the product suspension S are in the range of 5000 to 5 million m < ² > / product suspension S metric tons, preferably 10,000 to 5000000 m < ² > / product suspension S metric tons. A method characterized in that it exhibits a total particle surface area (SSA _total ) in the range, more preferably in the range of 70,000 to 500,000 m ² / S metric tonnes of product suspension.   The method according to claim 1 or 2, wherein at least one substance comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide of step b) is Selected from the group comprising marble, limestone, chalk, semi-calcined lime, calcined lime, dolomite limestone, calcareous dolomite, semi-calcined dolomite, calcined dolomite, and precipitated alkaline earth metal carbonates such as precipitated calcium carbonate And the method. 4. A method according to any one of claims 1 to 3, comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide of step b). Process, characterized in that the type of substance has a weight-median particle size (d ₅₀ ) in the range of 0.1 μm to 1 mm, preferably in the range of 0.7 μm to 100 μm. 5. A process according to any one of claims 1 to 4, comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide of step b). Process, characterized in that the kind of material has a specific surface area (SSA) in the range of 0.01 to 200 m ² / g, preferably in the range of 1 to 100 m ² / g.   6. A method according to any one of claims 1 to 5, comprising at least one alkaline earth metal carbonate and optionally at least one alkaline earth metal hydroxide of step b). A process characterized in that the kind of substance has a hydrochloric acid (HCl) insoluble content of 0.02 to 90% by weight, preferably 0.05 to 15% by weight, based on the total weight of the dry substance.   The method according to any one of claims 1 to 6, wherein the product suspension S obtained in step d) is in the range of 1 to 80% by weight relative to the total weight of the product suspension S; A process characterized in that it has a solids content preferably in the range of 3 to 50% by weight, more preferably in the range of 5 to 35% by weight.   8. The method according to any one of claims 1 to 7, wherein the water in step a) is distilled water, tap water, desalinated water, brine, treated waste water, or, for example, ground water, surface water or rain water. Natural water, selected from. The method according to any one of claims 1 8, CO ₂ of step c), carbon dioxide gas, liquid carbon dioxide, the solid carbon dioxide or carbon dioxide and at least one other gas A process selected from gaseous mixtures, preferably gaseous carbon dioxide. A method according to any one of claims 1 to 9, the amount of CO ₂ that is used to generate one type of alkaline earth metal bicarbonates said at least of 1mol in the aqueous solution, mol The unit is in the range of 0.5 to 4 mol, preferably in the range of 0.5 to 2.5 mol, more preferably in the range of 0.5 to 1.0 mol, most preferably in the range of 0.5 to 0.65 mol. A method characterized by that.   Method according to any one of claims 1 to 10, characterized in that the particle fragmentation step f) is a grinding and / or grinding step, preferably a grinding step. .   12. The method according to any one of claims 1 to 11, wherein the aqueous solution obtained in step e) or step f) containing at least one alkaline earth metal bicarbonate is 5 to 130 ° dH, Preferably having a hardness of 10 to 60 ° dH, most preferably 15 to 50 ° dH.   13. The method according to any one of claims 1 to 12, wherein the aqueous solution obtained in step e) or step f) containing at least one alkaline earth metal bicarbonate is 6.5 at 20 ° C. A process characterized in that it has a pH in the range of 9 to 9, preferably in the range of 6.7 to 7.9, most preferably in the range of 6.9 to 7.7.   14. The method according to any one of claims 1 to 13, wherein the aqueous solution obtained in step e) or step f) containing at least one alkaline earth metal bicarbonate is 1 to 700 mg as calcium carbonate. / 1, preferably having a calcium concentration of 50 to 650 mg / l, most preferably 70 to 630 mg / l. 15. The method according to any one of claims 1 to 14, wherein the aqueous solution obtained in step e) or step f) containing at least one alkaline earth metal bicarbonate is 1 to 200 mg as magnesium carbonate. / 1, preferably having a magnesium concentration of 2 to 150 mg / l, most preferably 3 to 125 mg / l.   16. The method according to any one of claims 1 to 15, wherein the aqueous solution obtained in step e) or step f) comprising at least one alkaline earth metal hydrogen carbonate is lower than 1.0 NTU. A method characterized in that it has a turbidity value, preferably lower than 0.5 NTU, most preferably lower than 0.3 NTU.   A method according to any one of claims 1 to 16, characterized in that at least step d) is performed at a temperature in the range of 5 to 55 ° C, preferably in the range of 20 to 45 ° C. Method. 18. The method according to any one of claims 1 to 17, wherein the aqueous solution obtained in step e) or step f) is
(X) calcium bicarbonate, preferably calcium bicarbonate having a calcium concentration of 25 to 150 mg / l as calcium carbonate, or (xx) magnesium bicarbonate, preferably carbonate having a magnesium concentration of> 0 to 50 mg / l Or (xxx) a mixture of calcium bicarbonate and magnesium bicarbonate, preferably a mixture having a total calcium and magnesium concentration of 25 to 200 mg / l as calcium carbonate and magnesium carbonate. . 19. The method according to claim 18, wherein the aqueous solution obtained in step e) or step f) is
Calcium bicarbonate having a calcium concentration of 45 mg / l as calcium carbonate, or a mixture of calcium bicarbonate and magnesium bicarbonate having a calcium concentration of 80 to 120 mg / l as calcium carbonate and a magnesium concentration of 20 to 30 mg / l as magnesium carbonate A method comprising the steps of:   20. A method according to any one of the preceding claims, characterized in that it is a continuous process.   20. The filtration device of step e) is a membrane filter, preferably a tube-type membrane filter having a pore size of 0.02 to 0.2 [mu] m, according to any one of claims 1 to 19 the method of.   22. A process according to any one of claims 1 to 21 for the preparation of precipitated alkaline earth metal carbonates and / or hydromagnesite, in particular for the preparation of precipitated calcium carbonate and / or hydromagnesite. Use of an aqueous solution comprising at least one alkaline earth metal bicarbonate obtained by   Use of an aqueous solution comprising at least one alkaline earth metal hydrogen carbonate obtained by the process according to any one of claims 1 to 21 for the mineralization of water. A method for mineralizing water,
I) the process of preparing the feed water,
II) a step of preparing an aqueous solution containing at least one alkaline earth metal bicarbonate; and III) a feed water of step I) and an aqueous solution containing at least one alkaline earth metal bicarbonate of step II) And obtaining mineralized water by combining them.   25. The method according to claim 24, wherein the aqueous solution comprising at least one alkaline earth metal bicarbonate in step II) is at least 3 ° dH, preferably at least 5 than the hardness of the feed water in step I). A method characterized by having a high hardness of ° dH.   26. A method according to claim 25, characterized in that the aqueous solution comprising at least one alkaline earth metal hydrogen carbonate of step II) has a hardness of at least 15 dH. A method for preparing a precipitated alkaline earth metal carbonate,
IV) a step of preparing an aqueous solution containing at least one alkaline earth metal hydrogen carbonate, and V) heating the aqueous solution containing at least one alkaline earth metal hydrogen carbonate in step IV) to prepare precipitated alkaline earth. And / or VI) adding at least one alkaline earth metal hydroxide or alkaline earth metal oxide to the solution of step IV) to obtain a precipitated alkaline earth metal carbonate. A method comprising the steps of:   28. The method of claim 27, wherein the precipitated alkaline earth metal carbonate is an amorphous alkaline earth metal carbonate such as amorphous calcium carbonate or amorphous magnesium carbonate, calcite form, aragonite form. Alternatively, a method characterized in that it is selected from vaterite crystalline calcium carbonate, magnesite and hydromagnesite, or a mixture thereof.

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